2) the PCB has been revised in order to provide a jumper to set the headamp gain in either LOW or HIGH position, as the regular ONE came with its headamp set to HIGH and this was a bit of a potential issue with low impedance/high sensitivity headphones for people who don't listen at loud volume.

I have the ST and bought the E1 to compare. The E1 one is better as an amp, but as a DAC I couldnt tell much difference. I ended up selling the E1 and getting an UberFrost and separate amps for specific headphones.

I guess it wouldn't mix well with a Audeze headphone. I already tried the LCD-2 with the STX and it didn't sound okay at all. With low gain you reach half the volume meter and it doesn't get any louder from there and starts to clip. with medium and high gain there's no more clip, but the distorsion is unbearable.

I'm a bit confused, I have been running my Asus Xonar Essence One using SPDIF from my Creative Titanum HD in order to get the CMSS:3D effects working while gaming, and I have always found the gain to feel quite weak / low..

So I got myself a Creative ZxR with its own built-in headphone amp to compare and they seem to feature much improved gain, but overall a bit lower audio quality. Might it be that the Asus Xonar Essence One is not running in High-Gain mode making it feel weak running my Sennheiser HD 650? There seems to be no way to verify or change the gain on the actual unit itself, I guess you might have some software options running the Xonar Essence One using USB, but like I said I'm running it through SPDIF in order to get the DSP from my Creative Titanium HD...

I'm not going to keep the Creative ZxR as I don't really like the sound signature, and the DSP feels very week compared to the Titanium HD, especially for gaming. CMSS:3D seems to do wonders compared to their new SBX Studio Pro which seems like a rebranded THX ThruStudio which I always have on my Titanium HD...

Going for Essence STX II is not an option either as I can't stand Dolby Headphones for gaming, that's why I got the Essence One a few months back in order to get the benefit of Creative's CMSS:3D DPS for gaming, while having the audio quality and amp from Essence One.. But like I said, the gain seems very thin..

Another things I'm really struggling with is the connection from my Titanium HD to the Essence One... Very often audio is simply not played back at all.. Especially notification sounds from Windows login, Skype notifications etc.. Is either not played at all, or I will hear the notification halfway through making it all sound fuzzy.. I can't seem to figure out what might be causing this, its not like the audio has any problems while playing back movies, games, during actual Skype voice chatting etc... But its almost like these notification sounds get lost while the computer is establishing communication with the DAC which is quite awkward and a little bit annoying.